Prior arts three-dimensional image projecting devices are disclosed in Japanese Laid-Open Patent Publication (TOKKAIHEI) No. 5-107504 and paper "PROGRESS ON THE HOLOGRAPHIC MOVIE PROCESS IN THE USSR", Three-dimensional Imaging (1977), SPIE Vol.120, respectively.
The three-dimensional image projecting device described in Japanese Laid-Open Patent Publication No. 5-107504 is so constructed that images with parallax from different directions are displayed on a plurality of liquid-crystal displays (LCD) arranged horizontally and the displayed images are projected on a retro-reflecting screen through a projection lens, Fresnel lens and convex mirror. The retro-reflecting screen is composed of a lenticular lens and diffusion reflecting surface. An observer can view a three-dimensional image by the effect of the parallax of the images. However, a three-dimensional image to be produced by the three-dimensional image projecting device is a stereogram using only the effect of parallax between the left and right eyes of the observer.
The three-dimensional image projecting device described in the paper "PROGRESS ON THE HOLOGRAPHIC MOVIE PROCESS IN THE USSR", Three-dimensional Imaging (1977), SPIE Vol. 120 is so constructed that a hologram image reproduced from hologram is projected onto a screen through a projection lens. The screen is multiplexed hologram of a concave mirror whereby a three-dimensional image is formed as three-dimensional images. The screen is a hologram of a multi-recorded concave mirror, which are observable by the same number of observers as the number of the multiplexed records. The device uses a double-recorded hologram of the concave mirror. Accordingly, an observer can view a three-dimensional image through an observing window while another observer can view a three-dimensional image through another observing window. The three-dimensional images observable by the observers are identical to each other.
However, the former of the above-mentioned prior arts is based on stereoscopic vision of a stereogram by using a parallax and lacks in adjusting function of another stereoscopic viewing mechanism. Accordingly, it may tire the eyes of the observer so much not to enjoy the video stereoscopic vision for a long time.
The latter prior art device provides a real image of an object observable by using all stereoscopic viewing mechanisms that may not tire the eyes of the observer. However, its viewing window (i.e., field of vision) is narrow and restricts the field of observing the three-dimensional image. To widen the visual field of this device, it is necessary to use projection lenses of a large diameter which is, however, expensive.